The present invention is directed to an apparatus and method for establishing an operating parameter for electrical power supply apparatuses. The present invention is especially directed to an apparatus and method for establishing shutdown output current for DC-to-DC power converter apparatuses. In most contemporary DC-to-DC power converter apparatuses, there is an inherent current limit involved in the operation of the apparatus. That is, beyond a certain point, the power generated by the converter device becomes substantially constant, so as output or load current (I) increases, the output voltage (V) decreases. When this condition is reached, it is frequently desireable for the apparatus to turn off. Turning off is desireable because the low output voltage is not adequate for the load, and the increased output current can harm the DC-to-DC converter. It is desirable for DC-to-DC power converter apparatuses to be flexible in their applicability to various products. Such flexibility allows a manufacturer of such apparatuses to reduce the number of discrete apparatus models that must be offered in order to provide a product line that addresses a wide range of possible applications. One aspect of such desired flexibility is to provide users, or customers, with a capability to control the output current limit for DC-to-DC power converter apparatuses. That is, users of DC-to-DC apparatuses desire that they may set the current limit for the apparatus. Such control has been made available to users of such apparatuses in the past, but there are problems with such earlier offerings, especially at low output current levels.
Earlier solutions to providing customer, or user control of the current limit for DC-to-DC power converter apparatuses involved an estimating methodology that introduced significant error into the turn-off point of the apparatus and risked uncontrolled, and therefore unanticipated shut down of the apparatus. Such earlier solutions introduced an offset to a programming signal in order to avoid nuisance shut down occurrences at low current level settings. The offset thus introduced adversely affected the accuracy of the apparatus response over a significant range of operation.
There is a need for an improved user programmable adaptive current shutdown method and apparatus for use with power supply apparatuses. Such a method and apparatus is especially needed in connection with DC-to-DC power converters at low output current levels.